Electron beam collector electrode for an electron beam tube

ABSTRACT

This invention relates to an electron beam collector electrode for an electron beam tube, in particular a transit-time tube, having a hollow body closed off by a collector base member in the electron beam direction. The electron beam collector electrode is designed to receive an electron beam and is especially a multistage collector. A star-shaped grid electrode extending substantially transverse to the electron beam direction and electrically insulated in respect to the base member of the collector is arranged in front of the base-member to suppress the secondary electrons.

11 ted States Patet [191 Wolfram Dec.9, 1975 ELECTRON BEAM COLLECTOR ELECTRODE FOR AN ELECTRON BEAM TUBE [75] Inventor: Roland Wolfram, Munich, Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin & Munich, Germany 22 Filed: Nov. 4, 1974 21 Appl. No.: 520,469

[30] Foreign Application Priority Data Nov. 8, 1973 Germany 2355902 [52] US. Cl. 315/538; 315/35; 315/393 [51] Int. Cl. H01] 23/02 [58] Field of Search 315/35, 5.35, 39.3, 3.6,

[56] References Cited UNITED STATES PATENTS 6/1942 Haeffm 315/538 3,368,104 2/1968 McCullough 315/538 3,644,778 2/1972 Mihran 315/538 3,702,951 11/1972 Kosmahl 315/538 3,780,336 12/1973 Giebeler 315/538 3,806,755 4/1974 Lien 315/538 Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or FirmHill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson 57 ABSTRACT Thisinvention relates to an electron beam collector electrode for an electron beam tube, in particular a transit-time tube, having a hollow body closed off by a collector base member in the electron beam direction.

The electron beam collector electrode is designed to receive an electron beam and is especially a multistage collector. A star-shaped grid electrode extending substantially transverse to the electron beam direction and electrically insulated in respect to the base member of the collector is arranged in front of the basemember to suppress the secondary electrons.

18 Claims, 3 Qrawing Figures US. Patent Dec. 9, 1975 Sheet 1 of 2 3,925,701

US. Patent Dec. 9, 1975 Sheet 2 of2 3,925,701

ELECTRON BEAM COLLECTOR ELECTRODE FOR AN ELECTRON BEAM TUBE BACKGROUND OF THE INVENTION 1. Field of the Invention In the art, a mesh grid uniformly contains grid elements with components extending circumferentially. Azimuthal elements of this kind are surrounded by equipotential surfaces which elastically reflect a substantial portion of the high velocity electrons passing in the proximity of the grid. These electrons are reflected along reverse paths back to the high potential electrodes. A small portion of the electron cloud manages to escape the influence of the high potential and is able to lease the collector, resulting in the reduction of the efficiency of a multi-stage collector. The primary electrons driven back into the interaction space give rise to unwanted oscillations.

2. Prior Art A collector of this kind has been described in IEEE Trans. Electron Devices, Volume ED-l9 No. l, Jan. 1972, pages 111-121. The grid provided there is designed as a coarse mesh grid, is at a potential lower than the base member, and is intended to prevent secondary electrons expelled from the base member from penetrating into the interaction space, to prevent them from generating parasitic oscillations in the tube.

Investigations carried out in relation to the present invention have shown that a grid of the known kind, in particular in transit time tube, does not reduce the tendency to oscillation to the expectation value even if the secondary electrons from the base member are fully inhibited. This is particularly evident in a multi-stage collector, where the efficiency is considerably less than optimum.

SUMMARY OF THE INVENTION In order to overcome these drawbacks, it is proposed in accordance with the invention that the grid of an electron beam collector should be designed purely as a star-shaped structure, with spoke-like members eminating from a base member and terminating at a point in space, the center of the star-shaped grid (star grid) being located at least approximately upon the axis of the incident electron beam, that is, the axis which the latter has at entry into the electron beam collector.

A mesh grid always contains grid elements with components extending circumferentially. Azimuthal elements of this kind are surrounded by equipotential surfaces which elastically reflect a significant proportion of the high velocity electrons penetrating to points near to the grid, along reverse paths reaching the electrodes of high potential or even managing to escape the collector altogether. Electrons which escape in this fashion clearly reduce the efficiency of a multi-stage collector whereas the primary electrons driven back into the interaction space give rise to unwanted oscillation.

A grid in accordance with the invention has practically no azimuthal parts at all. Thus, in the case of those electrons which may still be deflected by the grid along reverse paths, even after reflection, the outwardly directed radial components of the trajectory are at least approximately maintained.

In one embodiment of the invention, it is proposed that the members should in each case be rotated about the axis of their longitudinal extent similar as in the propeller blade art. The resultant pitch in the members additionally imparts a circumferential component to the trajectories of the reflected electrons, and thus allows outwardly acting centrifugal forces to take effect.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic lateral section of an electron beam collector in accordance with the invention;

FIG. 2 illustrates a partially cut away frontally elevated view of an isolated grid in accordance with the invention; and

FIG. 3 is a diagrammatic frontally elevated view depicting a modified grid in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In view of the above FIGS. 1-3, all non-essential components of an electron beam collector such as the electrical leads to the individual electrodes, have been omitted from the drawings.

In FIG. 1, a multi-stage collector for a traveling wave tube is illustrated, wherein said collector comprises essentially a hollow body 3 having a beam entry position 1, and at an opposite end a collector base member 2. The hollow body 3 comprises a series of electrodes 5, 6, 7, 8, 9 arranged in series linearly contiguous to each other in the electron beam direction and separated from each other by ceramic spacer rings 4. The electrode 5 has a metallic construction while the other electrodes and the base member are made of carbon. In order to insure that the carbon parts of the collector are vacuum-tight, they are circumferentially split at the level of the spacer rings 4, and provided with a metal insert 11 (as described in our earlier German Pat. Application No. P 22 44 267.7; VPA 72/1 155). The internal and external parts of the electrodes and of the base member produced by the splitting operation, have been given the references 21, 22; 61, 62; 71, 72; 81, 82; and 91, 92, respectively, in FIG. 1. Centrally inset in the base member 2 there is a null electrode 12. The null electrode 12 is electrically insulated from the base member 2 by a ceramic ring 13 and comprises a rod electrode 14 extending eccentrically and substantially into the collector cavity and a grid member 15.

In the operation of the tube, the null electrode 12,

. together with the rod electrode 14 and the grid member 15, function at cathode potential or at a similar low potential, while the other electrodes are at independent positive levels in relation to the null electrode 12. In the case of the collector illustrated, for example, the electrodes, in the sequence in which they have been numbered, could operate at respectively decreasing potentials of 12,000V, 10,000V, 8,000V, 6,000V, 4,000V, the base member at 2,000V and the null electrode at 0V, in relation to the cathode potential.

The electrodes projecting laterally into the collector cavity catch the electron incident therein and discriminate in relation to their velocities in order to minimize heat transfer losses to be dissipated and at the-same time achieve a high collector efficiency. Velocity-discrimination is reinforced by the eccentric rod electrode 14 which generates a strong transverse field while producing only a minor reduction in the axial potential in the electron beam direction.

To prevent secondary electrons produced by electron bombardment from straying into the interaction zone, the electrodes, with the exception of the base member, can be given a suitable arrangement. Secondary electrons leaving the base member are driven back by the grid 15. The grid in accordance with the invention is star-shaped with members 16 extending from a central point and terminating in free space. In the present case, main members 18 extending from the center 17 of the star grid, in each case, fork to form two branchmembers 19 whose widths as measured transversely to the electron beam direction, increase with increasing interval from the grid center 17, beyond a bend position. These measures provide for a potential coverage factor of constant density and compensate for any reduction in a potential density envelope at outer radii resulting from geometric considerations of the main member 18 as a function of increasing radii.

In order to insure that the coverage factor remains approximately the same throughout the complete coverage area, in addition to branching and increases in width, it is possible in accordance with the invention to employ a variety of different grid modifications. For example, the main member 18 can fork several times or can branch after the manner of an ice crystal, in the form of several branch members 19. In any branching variation, it is important to remember that the members 16 may not be circumferentially directed. In addition, the star grid can be given a variety of designs, such as monoplanar, curved, conical, angular or multiply folded radial section as shown in FIG. 1. In the preferred embodiment, the preferred shape, in terms of the intended opposing fields, can be calculated with good approximation from the known relationships governing the grid field. In addition, the members could also be rotated along their longitudinal axes as shown in FIG. 3 paterned after a propeller blade. The resultant pitch impacts to the trajectories of the electrons striking the members of the star grid, a circumferential component and thus enables outward-acting centrifugal forces to take effect. The incident electrons are then repelled less energetically and closer to the grid because only part of their forward momentum is converted to reverse momentum. A similar kind of rotation effect is also achieved if neighboring members are simply alternately bent at different angles to the electron beam direction.

Although the present invention has been described by reference to particular illustrative embodiments thereof, the illustrations and descriptions have only been provided as non-limiting examples. Many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. It is, therefore, intended that the patent warranted hereon cover all such changes and modifications as may reasonably and properly be included within the scope of the contribution to the art.

I claim as my invention:

1. In an electron beam collector for a transit-time tube to receive an electron beam incident on said electron beam collector having a hollow body closed off in a direction of the incident electron beam by a base member to form a cavity, and a grid located in said cavity in front of said base member and electrically insulated in relation thereto, extending transversely to the direction of the incident electron beam, the improvement of a star grid having a center and a plurality of radially extending members of definite width emanating wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases'as a function of increasing radius.

5. An electron beam collector as defined in claim 4, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.

6. An electron beam collector as defined in claim 1, wherein at least one of the widths of the radially extending members as measured transversely to the direction of the incident electron beam increases at least over a portion of the extending member as a function of increasing radius measured from the star grid center.

7. An electron beam collector as defined in claim 6, wherein at least one of the radially extending members have symmetrically branched members.

8. An electron beam collector as defined in claim 7, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.

9. An electron beam collector as defined in claim 8, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.

10. In an electron beam collector for an electron beam tube to receive an electron beam incident on said electron beam collector having a hollow body closed off in a direction of the incident electron beam by a base member to form a cavity, and a grid located in said cavity in front of said base member and electrically insulated in relation thereto, extending transversely to the direction of the incident electron beam, the improvement of I a star grid having a center and a plurality of radially extending members of definite width emanating from said center and terminating in a cavital space, wherein said center is located approximately on the axis of the incident electron beam at entry into said collector.

11. An electron beam collector as defined in claim 10, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.

12. An electron beam collector as defined in claim 10, wherein at least one of the radially extending members have symmetrically branched members.

13. An electron beam collector as defined in claim 12, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of 16. An electron beam as defined in claim 15, wherein at least one of the radially extending members have symmetrically branched members.

17. An electron beam collector as defined in claim 16, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.

18. An electron beam collector as defined in claim 17, wherein at least one of said radially extending members is selectively rotated about anaxis of its longitudinal extension and permanently set to conform to a desired pitch. 

1. In an electron beam collector for a transit-time tube to receive an electron beam incident on said electron beam collector having a hollow body closed off in a direction of the incident electron beam by a base member to form a cavity, and a grid located in said cavity in front of said base member and electrically insulated in relation thereto, extending transversely to the direction of the incident electron beam, the improvement of a star grid having a center and a plurality of radially extending members of definite width emanating from said center and terminating in a cavital space, wherein said center is located approximately on the axis of the incident electron beam at entry into said collector.
 2. An electron beam collector as defined in claim 1, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.
 3. An electron beam collector as defined in claim 1, wherein at least one of the radially extending members have symmetrically branched members.
 4. An electron beam collector as defined in claim 3, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.
 5. An electron beam collector as defined in claim 4, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.
 6. An electron beam collector as defined in claim 1, wherein at least one of the widths of the radially extending members as measured transversely to the direction of the incident electron beam increases at least over a portion of the extending member as a function of increasing radius measured from the star grid center.
 7. An electron beam collector as defined in claim 6, wherein at least one of the radially extending members have symmetrically branched members.
 8. An electron beam collector as defined in claim 7, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.
 9. An electron beam collector as defined in claim 8, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.
 10. In an electron beam collector for an electron beam tube to receive an electron beam incident on said electron beam collector having a hollow body closed off in a direction of the incident electron beam by a base member to form a cavity, and a grid located in said cavity in front of said base member and electrically insulated in relation thereto, extending transversely to the direction of the incident electron beam, the improvement of a star grid having a center and a plurality of radially extending members of definite width emanating from said center and terminating in a cavital space, wherein said center is located approximately on the axis of the incident electron beam at entry into said collector.
 11. An electron beam collector as defined in claim 10, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.
 12. An electron beam collector as defined in claim 10, wherein at least one of the radially extending members have symmetrically branched members.
 13. An electron beam collector as defined in claim 12, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.
 14. An electron beam collector as defined in claim 13, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch.
 15. An electron beam collector as defined in claim 10, wherein at least one of the widths of the radially extending members as measured transversely to the direction of the incident electron beam increases at least over a portion of the extending member as a function of increasing radius measured from the star grid center.
 16. An electron beam as defined in claim 15, wherein at least one of the radially extending members have symmetrically branched members.
 17. An electron beam collector as defined in claim 16, wherein at least one of the widths of the branched members as measured transversely to the direction of the incident electron beam increases as a function of increasing radius.
 18. An electron beam collector as defined in claim 17, wherein at least one of said radially extending members is selectively rotated about an axis of its longitudinal extension and permanently set to conform to a desired pitch. 